times farther from us at one time, than at another; and also seemeth to be alwayes of an equal bigness, although it ought to shew forty times bigger when nearest to us, than when farthest off.
Sagr.But in Jupiter, Saturn and Mercury, I believe that the differences of their apparent magnitudes, should seem punctually to answer to their different distances.
Salv.In the two Superiour ones, I have made precise observation yearly for this twenty two years last past:Mercury admitteth not of clear observations. In Mercury there can be no observation of moment made, by reason it suffers not it self to be seen, save onely in its greatest digrssieons from the Sun, in which its distances from the earth are insensibly unequal, and those differences consequently not to be observed; as also its mutations of figures which must absolutely happen in it, as in Venus. And if we do see it, it must of necessity appear in form of a Semicircle, as Venus likewise doth in her greatest digressions; but its discns is so very small, and its splendor so very great, by reason of its vicinity to the Sun, that the virtue of the Telescope doth not suffice to clip its tresses or adventitious rayes,The difficulties removed that arise from the Earths moving about the Sun, not solitarily, but in consort with the Moon. so as to make them appear shaved round about. It remains, that we remove that which seemed a great inconvenience in the motion of the Earth, namely that all the Planets moving about the Sun, it alone, not solitary as the rest, but in company with the Moon, and the whole Elementary Sphear, should move round about the Sun in a year; and that the said Moon withal should move every moneth about the earth. Here it is necessary once again to exclaim and extol the admirable perspicacity of Copernicus, and withal to condole his misfortune, in that he is not now alive in our dayes, when for removing of the seeming absurdity of the Earth and Moons motion in consort we see Jupiter, as if it were another Earth, not in consort with the Moon, but accompanied by four Moons to rovolve about the Sun in 12. years together, with what ever things the Orbs of the four Medicaean Stars can contain within them.
Salv.Why do you call the four jovial Planets, Moons?
Sagr.Such they would seem to be to one that standing in Jupiter should behold them;The Medicean Stars are as it were four Moons about Jupiter. for they are of themselves dark, and receive their light from the Sun, which is manifest from their being eclipsed, when they enter into the cone of Jupiters shadow: and because onely those their Hemispheres, that look towards the Sun are illuminated, to us that are without their Orbs, and nearer to the Sun, they seem alwayes lucid, but to one that should be in Jupiter, they would shew all illuminated, at such time as they were in the upper parts of their circles; but in the parts inferiour, that is between Jupiter and the Sun, they would from Jupiter be observed to be horned; and in a word they would, tothe
